Interposer

ABSTRACT

An interposer, comprising: (a) a planar substrate having top and bottom surfaces, the bottom surface defining at least one ferrule alignment structure, and fiber bores, each bore hole being in a certain position relative to the ferrule alignment structure and adapted to receive a fiber; (b) at least one ferrule having an end face and comprising one or more fibers protruding from the end face, and at least one alignment feature cooperating with the ferrule alignment structure to position the ferrule precisely on the bottom surface such that the fibers are disposed in the fiber bores and protrude past the top surface; and (c) at least one optical component having one or more optical interfaces and being mounted on the top surface such that each of the optical interfaces is aligned with one of the fiber bores and is optically coupled with a fiber protruding from the fiber bores.

FIELD OF INVENTION

The subject matter herein relates generally to fiber optic substrates,and more particularly, to a planar interposer with optical componentsmounted on one side and a fiber array mounted on the opposite side.

BACKGROUND OF INVENTION

Fiber optic components are used in a wide variety of applications. Theuse of optical fibers as a medium for transmission of digital data(including voice, interne and IP video data) is becoming increasinglymore common due to the high reliability and large bandwidth availablewith optical transmission systems. Fundamental to these systems areoptical subassemblies for transmitting and/or receiving optical signals.Optical subassemblies typically comprise an interposer. As used herein,an interposer functions as a substrate for optical, opto-electrical, andelectrical components and provides interconnections to optically and/orelectrically interconnect the optical/opto-electrical/electricalcomponents. There is a general need to simplify both the design andmanufacture of interposers. The present invention fulfills this needamong others.

SUMMARY OF INVENTION

The following presents a simplified summary of the invention in order toprovide a basic understanding of some aspects of the invention. Thissummary is not an extensive overview of the invention. It is notintended to identify key/critical elements of the invention or todelineate the scope of the invention. Its sole purpose is to presentsome concepts of the invention in a simplified form as a prelude to themore detailed description that is presented later.

In one embodiment, the invention relates to an interposer comprising:(a) a planar substrate having top and bottom surfaces, the bottomsurface defining at least one ferrule alignment structure, and one ormore fiber bores extending from the bottom surface to the top surface,each bore hole being in a certain position relative to the ferrulealignment structure and adapted to receive a fiber; (b) at least oneferrule having an end face and comprising one or more fibers protrudingfrom the end face, and at least one alignment feature cooperating withthe ferrule alignment structure to position the ferrule precisely on thebottom surface such that the fibers are disposed in the fiber bores andprotrude past the top surface; and (c) at least one optical componenthaving one or more optical interfaces and being mounted on the topsurface such that each of the optical interfaces is aligned with one ofthe fiber bores and is optically coupled with a fiber protruding fromthe fiber bores.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows one embodiment of the interposer of the present inventionin which ferrule fibers extend through vias in optical components tooptically connect the optical components.

FIG. 2 shows an embodiment similar to that of FIG. 1 but uses fiberstubs in the vias to facilitate optical connection with the opticalcomponents.

FIG. 3 shows an embodiment similar to that of FIG. 1 but uses hollowwave guides to facilitate optical connection with the opticalcomponents.

FIG. 4 shows an embodiment similar to that of FIG. 1 but staggers theoptical components to eliminate the need for vias in the opticalcomponents.

DETAILED DESCRIPTION

Referring to FIG. 1, one embodiment of an interposer 100 of the presentinvention is shown. The interposer 100 comprises a planar substrate 101having top and bottom surfaces 101 a, 101 b. The bottom surface 101 bdefines at least one ferrule alignment structure 102, and one or morefiber bores 103 extending from the bottom surface 101 b to the topsurface 101 a. Each bore hole 103 is in a certain position relative tothe ferrule alignment structure 102 and is adapted to receive a fiber113. The interposer also comprises at least one ferrule 110 having anend face 111 and containing one or more fibers 113 protruding from theend face 111. The ferrule 110 also comprises at least one alignmentfeature 112 cooperating with the ferrule alignment structure 102 of thesubstrate 101 to position the ferrule 110 precisely on the bottomsurface 101 b such that the fibers 113 are disposed in the fiber bores103 and protrude past the top surface 101 a. The interposer alsocomprises at least one optical component 120 having one or more opticalinterfaces 121 and being mounted on the top surface 101 a such that eachof the optical interfaces 121 is aligned with one of the fiber bores 103and is optically coupled with a fiber 113 protruding from the fiberbores. Each of these elements is considered in greater detail below.

The substrate 101 serves a number of purposes. Its primary purpose is tofunction as the backbone of the interposer 100 to support, secure, alignand interconnect the ferrule 110, optical components 120, and supportingelectrical circuitry 130. Accordingly, it should be a relatively rigidmaterial that is thermally stable, and suitable for being heated totemperatures typical in solder reflow applications. In one embodiment,the substrate also functions as an insulator for electrical circuitryand thus should be a good dielectric. Suitable materials that are bothrigid and relatively inexpensive include, for example, various types ofglass, ceramics, quartz, polysilicon, amorphous silicon, and silicon. Inone particular embodiment, the substrate 101 is glass, which has thebenefit of being particularly rigid, inexpensive, and a good dielectric.

The substrate 101 defines alignment features to ensure alignment betweenthe fibers 113 in the ferrule 110 and the corresponding opticalinterfaces 121 on the optical components 120. To this end, the substrate101 comprises ferrule alignment features 103 to align the ferrule 110 onits bottom surface 101 b. Alignment features for aligning ferrules arewell known and include, for example, alignment pins/guide holes,alignment sleeves, plug/socket structures, and pins with v-groovestructures. In the embodiment shown in FIG. 1, the substrate 101 definesone or more guide bores 102 to receive alignment pins 112 of theferrule. Such an alignment configuration is known in connection withmating MT ferrules. It should be understood that, while the substrate101 is shown having guide bores 102, the guide bores 102 may instead beoccupied with alignment pins and the alignment pins 112 in the ferrule110 be removed to leave an alignment hole in the ferrule available toreceive the alignment pin disposed in the substrate. In such anembodiment, if the alignment pins extend significantly beyond the bottomand top surfaces, they function not only to align the ferrule on thebottom surface 101 b, but also to align the optical components on thetop surface. Still other embodiments will be obvious to one of skill inthe art in light of this disclosure.

In one embodiment, the substrate 101 also functions to align the fibers113 with the optical interfaces 121 of the optical components by usingthe fiber bores 103 in the substrate 101 as shown in FIG. 1. In thisembodiment, the fiber bores 103 are disposed precisely with respect tothe guide holes. As discussed below, this is critical because theferrule holds the fibers in a precise location with the respect to thealignment features. Therefore, if the substrate defines fiber bores in aprecise location with respect to its ferrule alignment features, thefibers in the ferrule should align with the fiber bores in thesubstrate. The fibers 113 protruding from the ferrule end face 111 arereceived in the fiber bores 103 and are guided through the bore holes toa precise position on the top surface 101 a of the substrate. In theembodiment shown in FIG. 1, the fibers continue to extend from the topsurface to optically couple with the optical components as discussedbelow.

In one embodiment, the substrate also functions to align passively theoptical components 120 on the top surface 101 b such that the fibers 113optically couple with the optical interfaces 121 of the opticalcomponents 120. This may be accomplished using a variety of techniques.For example, in one embodiment, a pattern of contact pads are used thatpassively align the optical device during a reflow operation.Specifically, the optical device is provided with a certain pattern ofcontact pads on its bottom, the interposer has the same pattern on itstop planar surface. The optical device is then placed on the pads inrough alignment using known pick and place technology. Alignment betweenthe interposer and optical device is then achieved when the assembly isreflowed such that the surface tension of the contact pads causes thepatterns of the optical device to align over the pattern on theinterposer, thereby precisely positioning the optical device relative tothe fiber bores of the interposer. Such a mechanism is well known anddisclosed for example in U.S. Pat. No. 7,511,258, incorporated herein byreference.

In another embodiment, rather than or in addition to contact pads,fiducials on the interposer may be used to facilitate passive alignment.Fiducials are any structure or marking which provides for the passivealignment of the optical device. For example, the fiducials may bephysical structures protruding from the planar surface that provide aregister surface against which the edge of the optical device maycontact to be positioned correctly on the interposer. Alternatively, thefiducials may be markings to enable visual alignment of the opticaldevice on the interposer using a commercially-available, ultra-highprecision die bonding machine, such as, for example, a Suss MicroTecmachine (See, e.g., U.S. Pat. No. 7,511,258).

Additionally, a combination of fiducials and contact pads may be used.For example, the pads may be used to pull the optical device intocontact with the raised fiducials of the interposer. Still otheralignment techniques will be apparent to one of skill in the art inlight of this disclosure.

Therefore, the substrate 101 has one or more features for aligning theferrule 110 to the bottom surface 101 b and optical components 120 tothe top surface 101 a such that the fibers 113 of the ferrule opticallycouple with the optical components 120. The substrate may also supportelectrical circuitry for driving the optical components 120. Forexample, in FIG. 1, the top surface 101 a has circuitry 130 includingdrivers to operate the optical components 120. In one embodiment, theassociated circuitry 130 comprises traces and solder pads forinterfacing the interposer with a higher level flex circuit 131 orprinted circuit board.

The preparation of the substrate 101 can be performed in different ways.For example, the electrical circuitry can be applied thoughphotolithography as is well known, and the ferrule alignment featuresand fiber bores can be defined using techniques known for defining boresin ceramics, glass and other known substrates, including, for example,laser drilling, electrical discharge machining (EDM), reactive ionetching (RIE), water jet with laser oblation, sand blasting, and photostructuring with chemical etching.

The interposer of the present invention also lends itself to economicaland highly repeatable manufacturing. In one embodiment, a significantportion of the preparation of the interposer is performed at thewafer/panel stage. That is, rather than preparing each interposer as adiscrete component, multiple interposers can be prepared simultaneouslyon a wafer/panel. This is a known technique to facilitate large-scalemanufacturability. Benefits of wafer/panel fabrication include theability to define multiple features and components on multipleinterposers in one step. For example, most if not all of the criticalalignment relationships may be defined on the wafer/panel scale, oftenin just a few, or even a single, photolithography step. Specifically,the location of the traces, contact pads for the optical components, theguide bores and fiber bores may be defined in a single masking andetching step. In one embodiment, even the edges of the interposers aredefined in the same masking step. In other words, each edge of theinterposer is one half of a groove etched in the wafer/panel. Thewafer/panel is simply parted at the bottom of each groove to forminterposers with precisely controlled edges. This way, the distance fromthe edge of the interposer to critical features may be preciselycontrolled, often in a single step, thereby eliminating tolerance buildup and simplifying assembly manufacturing with the interposer by use ofthese precisely controlled edges. These advantages are expected toincrease as the size of wafers/panels and their handling capabilitiesincrease as well. Further economies may be realized by etching thesefeatures using the same photolithographic procedure. Although a singleetching procedure may be used, in certain circumstances, two or moreetching procedures may be beneficial.

The ferrule 110 functions to hold the fibers 113 in alignment relativeto the alignment feature 112. The ferrule may be configured to hold oneor a plurality of fibers. Ferrules are well known, and any known orlater-developed ferrule can be used providing that the ferrule caninterface with ferrule alignment features on the substrate. Suitableferrule configures include, for example, MT ferrules, MPO ferrules, andMT-RJ ferrules. In the embodiment of FIG. 1, the ferrule 110 is an MTferrule.

To effect optical coupling with the optical components, fibers 113extend from the end face 111 of the ferrule 110. The extent to which thefiber extends will depend on the configuration of the optical component,such as whether the optical components are stacked or whether theycomprise fiber stubs or optical waveguides as described below. In oneembodiment, the fibers 113 are laser cleaved to the appropriate length.Methods for preparing a cleaved fiber protruding from a ferrule areknown, and disclosed for example in U.S. Pat. No. 7,377,700, herebyincorporated by reference in its entirety. Furthermore, in an embodimentin which the fiber end face is laser cleaved, end-shaping techniques,such as those disclosed in U.S. Pat. No. 6,963,687 (hereby incorporatedby reference in its entirety), may be used to shape the fiber end facewith a lens or other structure to enhance optical coupling with theoptical interface 121 of the optical component 120. For example, for asingle mode fiber with an air gap between the fiber and opticalinterface 121, a slant or angle finish of the fiber end face will reduceback reflection.

The optical component 120 may be any known or later-developed componentthat can be optically coupled to a fiber. The optical device may be forexample: (a) an optoelectric device (OED), which is an electrical devicethat sources, detects and/or controls light (e.g. photonics processor,such as, a CMOS photonic processor, for receiving optical signals,processing the signals and transmitting responsive signals,electro-optical memory, electro-optical random-access memory (EO-RAM) orelectro-optical dynamic random-access memory (EO-DRAM), andelectro-optical logic chips for managing optical memory (EO-logicchips), lasers, such as vertical cavity surface emitting laser (VCSEL),double channel, planar buried heterostructure (DC-PBH), buried crescent(BC), distributed feedback (DFB), distributed bragg reflector (DBR);light-emitting diodes (LEDs), such as surface emitting LED (SLED), edgeemitting LED (ELED), super luminescent diode (SLD); and photodiodes,such as P Intrinsic N (PIN) and avalanche photodiode (APD)); (b) apassive component, which does not convert optical energy to another formand which does not change state (e.g., fiber, lens, add/drop filters,arrayed waveguide gratings (AWGs), GRIN lens, splitters/couplers, planarwaveguides, or attenuators); or (c) a hybrid device which does notconvert optical energy to another form but which changes state inresponse to a control signal (e.g., switches, modulators, attenuators,and tunable filters). It should also be understood that the opticaldevice may be a single discrete device or it may be assembled orintegrated as an array of devices.

The optical component 120 has at least one optical axis 122 along whichthe light propagates to/from the optical component. Because the opticalcomponent is typically planar and disposed over the substrate,generally, although not necessarily, the optical axis 122 is essentiallyperpendicular to the top surface 101 a. In some embodiments, it may bepreferable to use an optical component having an optical axis that isessentially parallel to the top surface 101 a. In such an embodiment, areflective surface in the optical component or in a discrete componentmay be used to bend the light between the fiber and the opticalcomponent. It should be understood that the optical component is notlimited to a single optical axis, and often an optical component willhave a plurality of optical axes as depicted in FIG. 1. The opticalinterface 121 is defined at each optical axis 122 on each opticalcomponent. For example, the optical component may have a plurality ofinput optical interfaces and a plurality of output optical interfaces.

Referring to FIG. 1, one embodiment of the interposer is shown in whicha plurality of optical components 120 are disposed on the top surface101 a. In this particular embodiment, one of the optical components 120is a CMOS photonics processor 125 with a heat sink 126. The opticalprocessor is optically connected to a memory stack 127 via opticalfibers 113 which are interfaced with the processor via ferrule 115 andinterfaced with the memory stack 127 via ferrule 116. (It should also beunderstood that the optical connection between the processor and thememory stack may be a direct connection or it may be through a starcoupler or other optical circuit (e.g., perfect shuffle) in which theprocessor 125 is optically connected to memory stacks on differentsubstrates and the memory stack 127 is likewise optically coupled andaccessible to other processors.) The memory stack 127 comprises a logicchip 128 and two or more DRAM 129 chips stacked on top. Although thestack depicted in FIG. 1 is a memory stack 127 other embodiments arepossible. For example, the stack may comprise an array of VCSELs.

The configuration of the optical interconnection among the opticalcomponents 120 in the stack may vary. For purposes of nomenclature,referring to FIG. 1, a stack of optical components comprises a topoptical component 123 and one or more lower optical components,including a bottom optical component 124. If the stack only has twooptical components, then it has a bottom and top component, wherein thebottom component is also referred to as a lower optical component.

As shown in the embodiment of FIG. 1, the lower optical components 124comprise one or more vias 143 aligned with the fiber bores 103. As shownin FIG. 1, fibers 113 extend through the vias 143 of lower opticalcomponents 124 to reach the optical component above them. In oneembodiment, the fibers extend through two or more aligned vias of two ormore lower optical components.

In FIG. 1, the fibers extending through the vias of the opticalcomponents extend from the ferrule. Other embodiments exist. Forexample, referring to FIG. 2, rather than have a fiber extend from theferrule end face all the way through multiple aligned vias, it may bepreferable in some applications to dispose a fiber stub 201 in thealigned vias 143. In one embodiment, a common fiber stub extends betweenaligned vias of two or more optical components. If fiber stubs are used,the fibers protruding from the ferrule may be cleaved an equal distancefrom the ferrule end face, but with sufficient protrusion to opticallycouple with the fiber stubs. As is known in the art, the opticalcoupling between the fiber and the fiber stub may be improved using arefractive index matching gel.

In yet another embodiment, the vias 143 are used as hollow waveguides301 as shown in FIG. 3. To improve the performance of the waveguides,they may be metal-coated as is known in the art. In such an embodiment,it may be preferable to close the gap between optical components toimprove the efficiency of the waveguides.

In yet another embodiment, the need for vias through lower opticalcomponents is reduced or eliminated by staggering the optical components420 as shown in FIG. 4. In this embodiment, one or more opticalinterfaces 421 of a given optical component 420 a are unobstructed byoptical components 420 b between the given optical component 420 a andthe top surface 101 a.

Still other configurations for optically coupling a stack of opticalcomponents with the fibers in a ferrule coupled to the substrate will beobvious to one of skill in the art in light of this disclosure.

While this description is made with reference to exemplary embodiments,it will be understood by those skilled in the art that various changesmay be made and equivalents may be substituted for elements thereofwithout departing from the scope. In addition, many modifications may bemade to adapt a particular situation or material to the teachings hereofwithout departing from the essential scope. Also, in the drawings andthe description, there have been disclosed exemplary embodiments and,although specific terms may have been employed, they are unlessotherwise stated used in a generic and descriptive sense only and notfor purposes of limitation, the scope of the claims therefore not beingso limited. Moreover, one skilled in the art will appreciate thatcertain steps of the methods discussed herein may be sequenced inalternative order or steps may be combined. Therefore, it is intendedthat the appended claims not be limited to the particular embodimentdisclosed herein.

What is claimed is:
 1. An interposer, comprising: a planar substratehaving top and bottom surfaces, said bottom surface defining at leastone ferrule alignment structure, and one or more fiber bores extendingfrom said bottom surface to said top surface, each bore hole being in acertain position relative to said ferrule alignment structure andadapted to receive a fiber; at least one ferrule having an end face andcomprising one or more fibers protruding from said end face, and atleast one alignment feature cooperating with said ferrule alignmentstructure to position said ferrule precisely on said bottom surface suchthat said fibers are disposed in said fiber bores and protrude past saidtop surface; and at least one optical component having one or moreoptical interfaces and being mounted on said top surface such that eachof said optical interfaces is aligned with one of said fiber bores andis optically coupled with a fiber protruding from said fiber bores. 2.The interposer of claim 1, wherein said ferrule alignment featurecomprises a guide bore in said bottom surface, and said alignmentfeature comprises an alignment pin protruding from said end face of saidferrule, said guide bore being adapted to receive said alignment pin toalign said ferrule on said bottom surface.
 3. The interposer of claim 2,wherein said guide bore extends from said bottom surface through saidtop surface.
 4. The interposer of claim 1, wherein said substratecomprises a ceramic or glass or silicon.
 5. The interposer of claim 1,wherein said optical interface and said fiber are in physical contact.6. The interposer of claim 1, wherein said optical component is aplurality of optical components stacked.
 7. The interposer of claim 6,wherein the stacked optical components comprise a top optical componentand one or more lower optical components, including a bottom opticalcomponent.
 8. The interposer of claim 7, wherein said lower opticalcomponents comprise one or more vias aligned with said fiber bores. 9.The interposer of claim 8, wherein one of said fibers extends througheach of said vias.
 10. The interposer of claim 9, wherein one of saidfibers extends through two or more aligned vias of two or more loweroptical components.
 11. The interposer of claim 8, wherein a fiber stubis disposed in said each of said vias.
 12. The interposer of claim 11,wherein a common fiber stub extends between aligned vias of two or moreoptical components.
 13. The interposer of claim 7, wherein the stackedoptical components are staggered such that one or more opticalinterferences of a given optical component are unobstructed by opticalcomponents between said given optical component and said top surface.14. The interposer of claim 1, wherein said optical component is atleast one of an optical processor, optical memory, logic chip, or aVCSEL or a Photo Detector.
 15. The interposer of claim 1, wherein saidoptical component comprises a stack of optical components and a bottomoptical component is a logic chip and at least two or more of the upperoptical components are DRAM chips.
 16. The interposer of claim 1,wherein said optical component is a CMOS photonics processor.
 17. Theinterposer of claim 1, wherein said ferrule is an MT ferrule.
 18. Theinterposer of claim 1 wherein said ferrule is an MT-RJ ferrule.